= Solution
\b[A transmissive mask is placed in contact with the resist, or a small distance above it for proximity printing.] Chromium-patterned glass or quartz is a typical mask. Illumination is normally collimated <ultraviolet> light, with refractive illumination optics used to prepare the beam.
There is no projection objective imaging a reduced mask pattern onto the resist: the mask shadows the resist approximately one-to-one. The finite gap in proximity printing introduces <diffraction> and limits edge sharpness; contact printing reduces that gap at the cost of mask wear and contamination risk.
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